Pumps of the kind referred to can be used for raising liquids through a height exceeding the barometric height. During that part of the cycle of the pressurising means in which the pressure in the duct is increasing, energy is transferred from the pressurising means to the storage means by the downward movement of liquid in a direction from the pressurising means towards the storage means. During that part of the cycle in which the pressure in the duct is decreasing, the potential energy in the storage means is imparted to the liquid as kinetic energy and, since the inlet valve remains closed whilst the pressure in the duct adjacent to the inlet exceeds the outside pressure, the liquid moves owing to its kinetic energy in a direction away from the inlet, that is upwardly. Liquid is thereby caused to flow through the outlet of the duct. Whilst the liquid is flowing through the outlet, the pressure within the duct adjacent to the inlet eventually falls to a sufficiently low value for the inlet valve to open, thereby allowing further liquid to be admitted to the duct.